Single camera vision system for logistics applications

ABSTRACT

This invention provides a single-camera vision system, typically for use in logistics applications, that allows for adjustment of the camera viewing angle to accommodate a wide range of object heights and associated widths moving relative to an imaged scene with constant magnification. The camera assembly employs an image sensor that is more particularly suited to such applications, with an aspect (height-to-width) ratio of approximately 1:4 to 1:8. The camera assembly includes a distance sensor to determine the distance to the top of each object. The camera assembly employs a zoom lens that can change at relatively high speed (e.g. &lt;10 ms) to allow adjustment of the viewing angle from object to object as each one passes under the camera&#39;s field of view (FOV). Optics that allow the image to be resolved on the image sensor within the desired range of viewing angles are provided in the camera lens assembly.

RELATED APPLICATIONS

This application is a continuation continuation of co-pending U.S.patent application Ser. No. 16/167,314, entitled of co-pending U.S.patent application Ser. No. 14/750,871, filed Jun. 25, 2015, entitledSINGLE CAMERA VISION SYSTEM FOR LOGISTICS APPLICATIONS, filed Oct. 22,2018, which is a continuation of co-pending SINGLE CAMERA VISION SYSTEMFOR LOGISTICS APPLICATIONS, now U.S. Pat. No. 10,116,870, issued Oct.30, 2018, the entire disclosure of each of which applications is hereinincorporated by reference.

FIELD OF THE INVENTION

This invention relates to machine vision systems and more particularlyto vision systems used in logistics applications to track packages andother objects moving through a handling facility, typically on aconveyor arrangement.

BACKGROUND OF THE INVENTION

Machine vision systems (also termed “vision systems”) that performmeasurement, inspection, alignment of objects and/or decoding ofsymbology (e.g. bar codes—also termed “IDs”) are used in a wide range ofapplications and industries. Such IDs are applied in a variety offormats (e.g. one-dimensional (1D), two-dimensional (2D), QR-code,DataMatrix, DotCode, etc.). These systems are based around the use of animage sensor (or “imager”), which acquires images (typically grayscaleor color, and in one, two or three dimensions) of the subject or object,and processes these acquired images using an on-board or interconnectedvision system processor. The processor generally includes bothprocessing hardware and software, in the form of non-transitorycomputer-readable program instructions, which perform one or more visionsystem processes to generate a desired output based upon the image'sprocessed information. This image information is typically providedwithin an array of image pixels each having various colors and/orintensities. In the example of an ID reader (also termed herein, a“camera”), the user or automated process acquires an image of an objectthat is believed to contain one or more barcodes. The image is processedto identify barcode features, which are then decoded by a decodingprocess and/or processor obtain the inherent alphanumeric datarepresented by the code.

A common use for ID readers is to track and sort objects (e.g. packages)moving along a line (e.g. a conveyor) in manufacturing and logisticsoperations. The ID reader can be positioned over the line at anappropriate viewing angle and distance to acquire any expected IDs onrespective objects as they each move through the field of view. Thefocal distance of the reader with respect to the object can vary,depending on the placement of the reader with respect to the line andthe size of the object. That is, a taller object may cause IDs thereonto be located closer to the reader, while a lower/flatter object maycontain IDs that are further from the reader. In each case, the IDshould appear with sufficient resolution to be properly imaged anddecoded. Thus, the field of view of a single reader, particularly inwith widthwise direction (perpendicular to line motion) is oftenlimited. Where an object and/or the line is relatively wide, the lensand sensor of a single ID reader may not have sufficient field of viewin the widthwise direction to cover the entire width of the line whilemaintaining needed resolution for accurate imaging and decoding of IDs.Failure to image the full width can cause the reader to miss IDs thatare outside of the field of view.

In certain cases, the field of view of the camera system can be widened(in a direction transverse to motion), often while narrowing theresolution (number of image pixels) in the motion direction byimplementing a field of view (FOV) expander. One such expander system isshown and described, by way of useful background in U.S. PublishedPatent Application No. US-2013-0201563-A1, entitled SYSTEM AND METHODFOR EXPANSION OF FIELD OF VIEW IN A VISION SYSTEM.

However this approach is cumbersome in many applications and is oftenmore suited to situations where the camera system must image arelatively wide line, rather than a line that includes both higher andlower boxes.

The problem is further illustrated in FIG. 1, which shows a cameraassembly 100 that is aligned along an optical axis OA with respect the amoving surface S. The surface moves in the direction of the page, andthus the width across the line is shown in this example. The cameraassembly 100 acquires an image of a scene containing a box or similarobject 110 with a top surface 112 that can contain one or more IDsrequiring decoding by the camera system and associated vision systemprocesses 120 (including an ID-decoding process 122). The height HB ofthe subject box 110 is shown as well as the width WB. In runtime, theactual height of the box can be varied between approximately 0 (a flatobject on the conveyor S) and a maximum height (approximately HB). Theviewing angle α of the camera assembly 100 should be set to image thefull width of the box at a given maximum height. Thus, a viewing anglea1 sufficiently covers the entire top surface 112 of the box 110.However, by setting the viewing angle to a1, the field of view issignificantly larger (often 1.5 to 2 times larger) than the field ofview needed to cover the dimensions of a flatter object with a heightcloser to 0 and width WB. These “wasted” image pixels on the opposingends of the image sensor's field of view is indicated by boundary points130. Thus, to adequately image a flatter object, a narrower viewingangle a2 can be employed.

Typically, there is a similar “waste” of pixels for flatter objectsalong the transport direction (into and out of the page of FIG. 1) dueto the need for a narrower viewing angle. In addition, waste of imagepixels in the transport direction results because the required filed ofview along this dimension is generally defined by the feature that mustbe captured in an image. That is, the image should span the entire widthof the object, but need only be tall enough to capture the height of theparticular features found within the overall object width (e.g. an ID).This is, because multiple images are captured as the object passes underthe camera (in the transport direction), and at least one or more of thecaptured images will contain the feature. In a typical logisticsID-reading application, the length of a barcode is usually 75 mm, so afield of view of 100 mm would sufficiently in this direction. However,most commercially available sensors have a width/height aspect ratio of4:3, 5:4 or 16:9, each of which ratios features a relatively largeheight dimension versus width. Thus, when such a sensor is used to coverthe width of the conveyor belt (and maximum object width at allheights), the field of view in the transport direction is usually muchlarger than desired.

Thus prior art, conventional single camera vision system for logisticsapplications disadvantageously use a large number of pixelsinefficiently. This inefficiency results from the fixed opening angle ofthe camera and the aspect ratio of the sensor. However, adjusting thecamera assembly's viewing angle to suit a given height of object ischallenging, both in terms of accuracy and speed of adjustment.

SUMMARY OF THE INVENTION

This invention overcomes disadvantages of the prior art by providing asingle-camera vision system, typically for use in logisticsapplications, that allows for adjustment of the camera viewing angle toaccommodate a wide range of object heights and associated widths movingrelative to an imaged scene. The camera assembly employs an image sensorthat is more particularly suited to such applications, with an aspect(height-to-width) ratio of approximately 1:4 to 1:8. The camera assemblyincludes a distance sensor, such as a laser range finder, stereo-optics,etc. to determine the distance to the top of each object. The cameraassembly employs a zoom lens that can change at relatively high speed(e.g. <10 ms) to allow adjustment of the viewing angle from object toobject as each one passes under the camera's field of view (FOV). Such alens can be illustratively based on moving-membrane liquid lenstechnology. Optics that allow the image to be resolved on the imagesensor within the desired range of viewing angles—as adjusted by thezoom lens—are provided in the camera lens assembly.

In an illustrative embodiment, a vision system for acquiring images offeatures of objects of varying height passing under a camera field ofview in a transport direction is provided. The vision system includes acamera with an image sensor having a height:width aspect ratio of atleast 1:4. A lens assembly is in optical communication with the imagesensor. The lens assembly has an adjustable viewing angle at constantmagnification within a predetermined range of working distances. Adistance sensor measures a distance between camera and at least aportion of object, and an adjustment module adjusts the viewing anglebased upon the distance. Illustratively, the adjustment module canadjust a focal distance of the lens assembly concurrently with theviewing angle. The lens assembly can have a variable lens element thatchanges focal distance based upon an input adjustment value, and thevariable lens element can comprise a liquid lens based on variousconcepts, such as the use of two iso-density fluids or a movingmembrane. Alternatively, an electromechanical variable lens can beemployed. Illustratively, the lens assembly has a front lens group and arear lens group, behind the front lens group, in which the front lensgroup is larger in diameter than the rear lens group, and wherein thevariable lens element is located behind the rear lens group. The frontlens group can include a front convex lens and a rear composite lens.The rear lens group can have a composite lens. Illustratively, anaperture having a predetermined diameter is located between the frontlens group and the rear lens group. This enables the system to operatewith a small-diameter, commercially available variable lens. Inembodiments, a front lens of the front lens group and a front lens ofthe rear lens group are separated by approximately 75 millimeters andthe aperture has a diameter of approximately 4 millimeters. Thesemeasurements are highly variable in various implementations. The visionsystem can also include a vision processor that analyzes the featuresand performs a vision system task based upon the features. Inembodiments, the features are ID features, and the vision processorincludes an ID decoder module. Illustratively, the camera is a singleunit that images objects within a field of view thereof having varyingheights and an ID located thereon. The camera can be arranged to image atop side of an object in relative motion, the top side being within apredetermined range of heights, and the object can be arranged on amoving conveyor. Alternatively, the camera can be arranged to moverelative to a stationary or moving object. The top side of the objectcan include at least one ID thereon and the vision system can include avision system processor that includes an ID decoder module. The distancesensor can be based on at least one of LIDAR, sonar, stereo imaging, alight curtain and laser range-finding. Additionally, the image sensorcan define a height:width aspect ratio of at least approximately 1:8.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention description below refers to the accompanying drawings, ofwhich:

FIG. 1 is a diagram of an object (box) of predetermined width on amoving conveyor line imaged by a vision system showing relative viewingangles at minimum and maximum height, by way of useful background;

FIG. 2 is a diagram of a single camera vision system according to anillustrative embodiment acquiring an image of an object having a firstheight on a moving conveyor line;

FIG. 3 is a diagram of a single camera vision system according to anillustrative embodiment acquiring an image of an object having a secondheight, lower that the first height (FIG. 2) on a moving conveyor line;

FIG. 4 is a side cross section of a lens arrangement and imager for usein the single camera vision system of FIGS. 2 and 3, according to anillustrative embodiment;

FIG. 5 is a block diagram showing an exemplary circuit arrangement forcontrolling adjustment of one or more variable/liquid lens assembliesaccording to an illustrative embodiment; and

FIG. 6 is a side cross section of the lens arrangement and imager ofFIG. 4 showing a constant field of view FOV for each of two differentworking distance settings with similar magnification.

DETAILED DESCRIPTION

Reference is made to FIG. 2, which depicts a logistics arrangement 200,which includes a single vision system camera 210 that can include anon-board or remote processor 212 with an associated vision systemprocess/processor 214, and in this embodiment, an ID decoderprocess/processor 216 is included to identify, decode and generate data218 from an ID (e.g. a 1D or 2D barcode, etc.). This data 218 isprovided a data handling system 220 to perform one or more data handlingtasks including, but not limited to tracking/routing of items, qualitycontrol, and item-acceptance/rejection. These tasks can be performed bya downstream computing device (e.g. a PC, server or cloud-computingarrangement, and/or by specific mechanisms, such as a conveyor system219 with sorting gates that direct objects in response to data containedin those objects' respective IDs.

Images are acquired by an image senor, or “imager”, 230 from lightfocused from the imaged scene by a camera lens assembly 240. Asdescribed below, the lens assembly includes a quick-acting auto-focusand auto-adjust mechanism that responds distance measurements andthereby rapidly adjusts the lens assembly to the proper focus andviewing angle for an object of a predetermined height. The arrangement200 includes, in the overall processor 212, a focus/viewing-angleadjustment process(or) 242 that provides adjustment information to thecamera 230 and/or lens assembly 240.

In the example of FIG. 2, an object (e.g. a box or package) A has aheight HA for which the top surface TA is fully imaged using a focusangle α1. Typically, this viewing angle is sufficient to cover the widthof the package at the height HA (in the direction orthogonal to thedepicted upstream-to-downstream motion/transport direction indicated byarrow M). The viewing angle α1 and associated focal distance is setbased upon a distance measurement dA from the camera image plane (orother camera-based reference point) to the object top surface TA. Adistance-measuring device 250 determines the distance dA. In thisembodiment, it is located upstream of the camera at a predeterminedposition that facilitates registration of object height data within thevision system in advance of arrival of the object A at the camera fieldof view. The conveyor 219 can be operatively connected to an encoder orsimilar motion-tracking device that provides encoder data 260 (relativeto conveyor motion) to the processor 212. This data can be used to timearrival of objects at the field of view after they are detected by, forexample, the distance-measuring device 250. Illustratively, thedistance-measuring device 250 can be implemented using a variety oftechnologies—for example, a sonar or LIDAR system, stereoscopic imaging,a light curtain or combination of such technologies. While not shown,the arrangement 200 can include appropriate illumination, implemented asan integrated unit with the camera 230 and/or separately mounted.

One or more of the sides of the object A can include one or more IDs orsimilar data structures (indicated by circled region IDA), respectively.These IDs are desirably captured by the vision system camera 210 andassociated processor 212. Referring to FIG. 3, an object B withlower-height HB (than the height HA of the first object A) is showntransported by the conveyor 219 into the field of view of the camera210. The distance-measurement device 250 reports a distance dB from thetop surface TB. In this example, the distance dB is greater than dA,indicating a lower-height object. Thus, the viewing angle α2 is lowerthan the angle α1. The angle adjustment between α2 and α1 is directed bythe processor based upon the distance measurement. Thefocus/viewing-angle adjustment process(or) 242 can employ a variety oftechniques to provide the desired viewing angle adjustment value α. Notethat the maximum viewing angle α is defined generally by the width ofthe conveyor (e.g. conveyor belt), corresponding to WFOV1 and WFOV2 andthe height of the largest object. The desired resolution of the visionsystem camera is defined by the smallest feature at the greatestdistance, generally controlled by the height of the smallest/lowestobject and smallest ID thereon. Note that in most logisticsapplications, the field of view at the level of the conveyor is at least1.5 to 2 times larger than needed to cover the width of the conveyer atmaximum object height. Thus, for any object on the conveyor that is lessthan maximum height, failure to adjust the viewing angle essentiallyresults in wasted pixels for the portions of an acquired image residingoutside the edges of the conveyor and object.

To determine the viewing angle α for a given distance d and apredetermined maximum conveyor width w (corresponding to the field ofview that fully images the conveyor width) the following equation:α=arctan(w/d)The adjustment process 242 can use this straightforward equation tocompute the viewing angle setting in the lens assembly 240. Likewise,the distance d can be used to control focus within the lens assemblyusing an appropriate equation. In alternate embodiments, equations canbe expressed in one or more associated lookup tables in which a value dis mapped to a stored coefficient.

Note, as used herein various directional and orientational terms such as“vertical”, “horizontal”, “up”, “down”, “bottom”, “top”, “side”,“front”, “rear”, “left”, “right”, “length”, “width”, “height”, and thelike, are used only as relative conventions, and not as absoluteorientations with respect to a fixed coordinate system, such as theacting direction of gravity.

It is also contemplated that the sensor 230 (FIG. 2) can be implementedusing an aspect ratio that is customized to this application. Ingeneral, the height of the sensor in the transport direction can besignificantly smaller than the width since multiple images can beacquired as an object moves along the transport direction, ensuring thatone or more images can fully capture the ID in this direction. However,the sensor should fully image the entire width of the conveyor andassociated object in each acquired image since there is no relativemovement of objects in the width direction that would otherwise enablemultiple images to stitch together a full view of an object.Illustratively a sensor having a height:width aspect of between 1:4 and1:8 is desirable. More generally an aspect ration of “at least” 1:4 andpotentially “larger” (e.g. 1:6, 1:8, etc.) is desired in variousembodiments. Those of skill will recognize that sensor manufacturers,such as CMOSIS of Belgium, can produce sensors with such specializedaspect ratios. Alternatively a conventionally sourced 16:9 aspect sensorcan be used in various embodiments to achieve improved performance inthe depicted logistics arrangement.

A numerical example of the required number of pixels in a typicallogistics application is now described. Typically, in a conventionalarrangement, appropriate imaging of an 80 cm object by a camera mounted160 cm above the conveyor requires a sensor of approximately 6400×3200pixels, totaling 23 Mpixels. This assumes an ID having a size of 10MILand 1 PPM resolution. By employing an adjustable-viewing-anglearrangement according to an embodiment with an 8:1 sensor with 3200×400pixels, the total pixel count is approximately 1.44 Mpixels. Thisarrangement results in a substantially lower pixel count, therebyallowing for faster processing of images and a less involved sensorinterface.

The adjustment process(or) 242 is particularly arranged to enableadjustment of both viewing angle and focal distance (focus)concurrently. This can be accomplished using one or more variable focuslenses as described below. In general, it is recognized that at theranges specified above, the focal distance and viewing angle tend to beclosely correlated.

Reference is now made to FIG. 4, which shows the lens assembly 240according to an illustrative embodiment in further detail. This lensassembly is illustratively based upon a fast-acting focal lengthadjustment using a liquid lens. The liquid lens can be based upon avariety of technologies (i.e. two isodensity fluids with a boundarylayer—available generally from Varioptic of France and moving membranetechnology—available generally from Optotune of Switzerland. Movingmembrane lens technology is employed in the lens assembly of theillustrative embodiment.

Reference is now made to FIG. 4, which shows an illustrative opticalarrangement (lens assembly) 400 (e.g. an integrated lens assembly forattachment to a vision system camera housing using an appropriate base,such as C-mount, M12, etc., threaded base 410) that provides a constantFOV at varied working distances according to illustrative embodimentsherein. The base 410 allows the lens assembly to reside at apredetermined distance from the imager 412, which provides the desiredFOV and working distance. It is expressly contemplated that the opticalarrangement can be constructed in a variety of manners that rely inwhole, or in part, upon ordinary skill, and the depicted arrangement isillustrative of such varied arrangements. The lens assembly can includean appropriate electrical connector to interface with the camera bodyand provide appropriate signals to and from the variable (liquid) lensand other components (e.g. a temperature probe, etc.)

The lens assembly 400 includes a (rear) liquid (or other variable) lensgroup 430, consisting of the liquid lens unit (described above-indicatedby dashed box 432) and associated lenses 434 and 436 that focus thereceived light from the front lens group 440. The front lens group 430defines an enlarged diameter DFG relative to the rear lens groupdiameter DRG. Also notably, the assembly 400 includes an aperture 450that can be positioned at an appropriate location along the optical axisOA) to compensate for the relatively small diameter (e.g. 10 millimetersor less) of the liquid lens assembly 432. The rear lens group 430 inthis embodiment illustratively consists of a front convex lens 434 andmatched concave lens 436 that collectively define a compound lens. Thefront lens group 440 comprises a front convex lens 442 and a rearcomposite convex and concave lens 444 and 446, respectively. In anembodiment the approximate lens parameters for lenses 434, 436, 442,444, 446, and (aperture) 450 are as follows:

Lens Reference Distance to Next No. Focal length Diameter Surface 44249.604 mm 38 mm  4 mm 444 −47.675 mm 26 mm  0 mm 446 −1930.735 mm 26 mm45 mm 450 —  4 mm 30 mm 434 34.7 mm 20 mm  0 mm 436 407.456 mm 20 mm  2mm

The lenses in the two groups 430 and 440 are spaced to provide thedepicted FOV (FOV1) at the desired range of working distances. In thisillustrative arrangement, the lens groups are separated by a distanceDLG of approximately 75 mm along the optical axis OA. By way of furthernon-limiting example, the radii of curvature and thickness of each lenscan be defined as follows (where “front” is facing toward an object and“rear” is facing toward the image sensor, and the (+/−) sign of theradius of curvature represents relative direction of the curvature):

Illustrative Thickness Lens Radius of Lens to Next Reference SurfaceCurvature Material Surface 442 Front 74.78 mm N-SF11 16.00 mm 442 Rear−74.78 mm N-SF11  4.00 mm 444 Front −27.82 mm N-BAF10  3.00 mm 444 Rear19.65 mm N-BAF10 0.00 446 Front 19.65 mm N-SF10  5.50 mm 446 Rear 201.68mm N-SF10 45.00 mm 450 Front — Varied 30.00 mm 450 Rear — Varied 434Front 21.17 mm N-BAF10 11.04 mm 434 Rear −16.08 mm N-BAF10  0.00 mm 436Front −16.08 mm N-SF10  3.00 mm 436 Rear −118.66 mm N-SF10  2.00 mm

Note that the above-described lens (and aperture) parameters should betaken by way of non-limiting example in an illustrative embodiment ofthe lens assembly employed in the vision system. For example,illustrative lens materials are provided as this affects opticalperformance, but a wide range of materials with various properties canbe employed and lens shapes can be modified in accordance with skill inthe art to accommodate different material properties. The aperturematerial can be varied as appropriate (e.g. polymer, metal, etc. withappropriate thermal stability. The listed lens parameters can also varybased upon differences in working distance range, viewing angle range,variable lens specifications (e.g. diameter, focal range) and/orrelative diameters of the lenses in each lens group. The parameters ofone or more lens (and aperture) components, and their relative spacingalong the optical axis can be varied using conventional opticsprinciples to accommodate changes in one or more of these parameters andmeasurements.

Referring again to FIG. 4, the liquid (variable) lens 430 is controlledby (e.g.) the vision processor and associated vision process 212 basedupon the focus angle adjustment process(or)/module 242 describedgenerally above. The focus angle adjustment process(or)/module 242communicates with a variable (e.g. liquid) lens controlprocess(or)/module 460 that can be part of the overall vision processor212, or can be a separate unit. As described above, the vision processor212 and focus angle adjustment module 242 receive input of distanceinformation 470 from an appropriate distance-measurement arrangement,which typically determines the height of the top surface of the objectunder inspection. With further reference to FIG. 5, the distanceinformation 470 is used to perform an adjustment computation using acomputation module 510 that is part of the variable lens control module460 and overall focus angle adjustment module. The computation module510 can define an equation-based engine that computes the adjustmentvalue for the lens based upon the input distance. Alternatively, thecomputation module can employ a look-up table that relates lensadjustment values (focal distances) to measured input distance andselects the appropriate adjustment value based upon the closest measureddistance (or an interpolation between a plurality of closest measureddistances. The lens adjustment value defines an input current and/orvoltage 520 that drives the position/focus of the lens motor 530. Thismotor can include a magnetic coil or other actuation device appropriateto the mechanism of the lens. The computation module 510 can base itscalculations on various adjustment parameters 540 that take intoaccount, for example, the temperature of the lens system and optics, theintrinsic and extrinsic parameters of the camera, and/or any specificcharacteristics of the lens over the working range.

Optionally, the variable lens control 460 can base adjustment or confirmadjustment using feedback 550 from the acquired image of the object.This can be used to refine adjustment as appropriate. Various auto-focusalgorithms—for example those that attempt to establish a crisp imagebased upon edge detection—can be employed.

FIG. 6 shows the optics arrangement 400 at two working distances, dB anddA, in which a similar field of view FOV1 and constant magnification isdefined for each working distance. This is based on the arrangement ofoptics in combination with the variable lens. To maintain the field ofview FOV1 at each distance dB and dA, the respective viewing angle α1and α2 is varied as shown (with a wider angle for a closer workingdistance and a narrower angle for a further working distance). Thesefocus settings are achieved by varying the variable (e.g. liquid) lensassembly 432 using specified adjustment values, AV1 and AV2,respectively. Other angles can be achieved using appropriate adjustmentvalues as described above.

It should be clear that the lens assembly defined hereinabove enablesthe use of a single camera assembly for use in imaging a wide range ofobject heights by allowing rapid and accurate variation of the viewingangle with constant magnification throughout the desired range ofworking distances.

The foregoing has been a detailed description of illustrativeembodiments of the invention. Various modifications and additions can bemade without departing from the spirit and scope of this invention.Features of each of the various embodiments described above may becombined with features of other described embodiments as appropriate inorder to provide a multiplicity of feature combinations in associatednew embodiments. Furthermore, while the foregoing describes a number ofseparate embodiments of the apparatus and method of the presentinvention, what has been described herein is merely illustrative of theapplication of the principles of the present invention. For example,Note also, as used herein the terms “process” and/or “processor” shouldbe taken broadly to include a variety of electronic hardware and/orsoftware based functions and components. Moreover, a depicted process orprocessor can be combined with other processes and/or processors ordivided into various sub-processes or processors. Such sub-processesand/or sub-processors can be variously combined according to embodimentsherein. Likewise, it is expressly contemplated that any function,process and/or processor here herein can be implemented using electronichardware, software consisting of a non-transitory computer-readablemedium of program instructions, or a combination of hardware andsoftware. Additionally, where the term “substantially” or“approximately” is employed with respect to a given measurement, valueor characteristic, it refers to a quantity that is within a normaloperating range to achieve desired results, but that includes somevariability due to inherent inaccuracy and error within the allowedtolerances of the system. Accordingly, this description is meant to betaken only by way of example, and not to otherwise limit the scope ofthis invention.

What is claimed is:
 1. A vision system for acquiring images of featuresof objects passing through a camera field of view, the vision systemcomprising: a camera with an image sensor; a lens assembly comprising afront lens group and a rear lens group, the rear lens group comprising avariable lens element and the front lens group comprising a front convexlens and a rear composite lens, the lens assembly having an adjustableviewing angle at a constant magnification within a predetermined rangeof working distance; and a processor in communication with the imagesensor and the lens assembly and configured to: receive a distancemeasurement corresponding to a distance between the camera and at leasta portion of an object; and adjust the viewing angle based upon thedistance measurement.
 2. The vision system of claim 1, wherein thecamera field of view corresponds to a portion of a conveyor surface. 3.The vision system of claim 2, further comprising a distance-measuringdevice configured to: measure the distance between the camera and the atleast the portion of the object; and provide the distance measurement tothe processor.
 4. The vision system of claim 3, wherein thedistance-measuring device is positioned upstream of the camera withrespect to a conveyance direction of the conveyor surface.
 5. The visionsystem of claim 1, wherein the processor receives the distancemeasurement prior to the object entering the camera field of view. 6.The vision system of claim 1, wherein adjusting the viewing anglecomprises determining an adjustment value for the lens assembly based onat least the distance measurement, via a predefined equation or apredefined lookup table.
 7. The vision system of claim 1, whereinadjusting the viewing angle comprises: determining if the distancemeasurement is greater than a first distance measurement; upondetermining that the distance measurement is greater than the firstdistance measurement, decreasing the viewing angle; and upon determiningthat the distance measurement is less than the first distancemeasurement, increasing the viewing angle.
 8. The vision system of claim1, wherein the processor is further configured to: acquire an image ofthe object via the camera; identify an ID within the image; and decodeand generate data from the ID.
 9. The vision system of claim 1, whereinthe processor is further configured to: receive encoder data indicativeof the object moving with respect to the camera; and determine, for theobject, a time of arrival within the camera field of view.
 10. Thevision system of claim 9, wherein the processor is further configured toacquire an image of the object via the camera, based on the time ofarrival and the distance measurement.
 11. The vision system of claim 1,wherein the lens assembly is configured to adjust the viewing angle inless than 10 milliseconds.
 12. The vision system of claim 1, wherein thevariable lens element comprises a liquid lens.
 13. The vision system ofclaim 1, wherein the processor is further configured to adjust a focaldistance of the lens assembly concurrently with the viewing angle. 14.The vision system of claim 1, wherein the image sensor defining aheight:width aspect ratio of at least 1:4.
 15. The vision system ofclaim 1, wherein the rear lens group includes a composite lens.
 16. Thevision system of claim 1, wherein the distance between the camera and atleast a portion of an object comprises one of: a distance between acamera image plane and the portion of the object, or a distance betweena camera-based reference point and the portion of the object.
 17. Avision system for acquiring images of features of objects passingthrough a camera field of view, the vision system comprising: a camerawith an image sensor; a lens assembly comprising a front lens group anda rear lens group, the rear lens group comprising a variable lenselement and the front lens group comprising a front convex lens and arear composite lens, the lens assembly having an adjustable viewingangle at a constant magnification within a predetermined range ofworking distance; and a processor in communication with the image sensorand the lens assembly and configured to: receive distance informationcorresponding to a distance between the camera and at least a portion ofan object; and adjust the viewing angle based upon the distanceinformation.